The Japanese patent application published under the No. JP-07-214968 discloses a writing instrument comprising an ink reservoir, a roller, a passage connecting the reservoir to the roller, and a valve mounted to move between a closed position in which it closes the passage, and open position in which it puts the reservoir into communication with the roller. A porous element is interposed in the passage between the roller and the valve, which valve is pierced by a hole that serves, in the open position, to allow the ink to flow from the reservoir towards the porous element, which porous element in turn inks the roller.
That type of writing instrument can give satisfaction, but it nevertheless presents a certain number of drawbacks.
Firstly, as can be seen in FIGS. 1 and 2 of the above-mentioned application, part of the roller is received in the passage provided for passing the flow of ink. In order to allow the roller to rotate freely, it can be understood that it is necessary to provide clearance between the roller and the passage. This leads to a risk of ink that is too fluid penetrating into said clearance and overflowing the contact zone between the roller and the support against which the roller is pressed, thereby leading to marks and smudges.
Furthermore, it can happen that the valve and/or the porous element become jammed in the passage, either in the closed position (in which case the ink no longer flows), or else in the open position (in which case the instrument leaks permanently), both to the detriment of proper operation of the writing instrument.